Tapered roller bearing with minimum heat generating characteristics

ABSTRACT

A tapered roller bearing has shallow circumferentially extending grooves in the tapered raceways of its cup and cone. Those grooves prevent full line contact between the frustoconical side surfaces of the tapered rollers and the tapered raceways and this in turn reduces the elastohydrodynamic oil film. The reduction of the elastohydrodynamic oil film minimizes the generation of heat within the bearing. The cup is further provided with annular channels through which oil is circulated to dissipate heat from the bearing.

United States Patent 1151 3,698,777 McCoy 1 51 0a. 17, 1972 [54] TAPEREDROLLER BEARING WITH 1,884,395 10/1932 Tyson ..308/214 MINIMUM HEATGENERATING 2,071,628- 2/1937 Hedcock ..308/2l4 CHARACTERISTICS v [72]Inventor: Wyn Eugene McCoy, Canton, Ohio ggzfg gzxxsgraii ggz AssigneeiThe Timken p y, Canton, Attorney-Gravely, Lieder & Woodruff Ohio 221Filed: Dec. 8, 1970 [57] ABSTRACT [21 1 AWL No; 96,189 A tapered rollerhearing has shallow circumferentially extending grooves in the taperedraceways of its cup and cone. Those grooves prevent full line contact[52] [1.8. CI. ..308/l87 between the frustoconical Side Surfaces of thetapered [51] Ilft. CI ..Fl6c 33/66, F166 33/00 toners and the taperedraceways and this in tum [58] of Search 308/187 reduces theelastohydrodynamic oil film. The reduc- 0 l 0 tion of theelastohydrodynamic oil film minimizes the generation of heat within thebearing. The cup is [5 6] References cued further provided with annularchannels through which UNITED STATES PATENTS oil is circulated todissipate heat from the bearing. 593,188 10/1897 Barker ..388/l87 10Claims, 3 Drawing Figures PATENTEDnmmen 3698.777

FIG 2 6 49 I 51 FIG.3 w

40 17 42 v 34 I I 40 i INVENTOR I WYN E. MCCOY ATTORNEYS BACKGROUND OFTHE INVENTION This invention relates in general to bearings and moreparticularly to a tapered roller bearing which generates a minimumamount of heat in operation.

In the operation of a precision machine tool the temperaturedifferential between various components and parts of the tool is animportant consideration, for any changes in temperature effect adimensional change in the tool itself, and this produces errors intooling setups. One of the major sources of heat in a machine tool isthe bearings, and in the case of tapered roller bearings, the heat isattributable primarily to the formation of an elastohydrodynamic oilfilm at the full line contact between the frustoconical surfaces of thetapered rollers and the opposed tapered raceways of the cup and conealong which the rollers roll.

The problem is particularly acute in relation to those bearings whichform' the journals for critical machine tool parts such as the spindlewhich drives the cutting tool or workpiece, for the heat generated inthese bearings is concentrated in the areas of the machine whereexpansion and contraction will cause the greatest errors in toolingset-ups. Consequently, the temperature of machine tool spindle bearingsand the like must be maintained substantially constant. Moreover, it isdesirable to reduce the generation of heat to an absolute minimum and toquickly dissipate that heat which is generated in order to have themachine tool operate close to room temperature. Of course, when themachine tool operates at room temperature, tooling set-ups may also bemade at that temperature.

While machine tools are perhaps most adversely affected by thegeneration of-heat in rolling element bearings, the problem alsopresents itself in other machinery such as printing presses and coatingmachines.

SUMMARY OF THE INVENTION One of the principal objects of the presentinvention is to provide a tapered roller bearing which reduces theelastohydrodynamic film between the rollers and raceways to a minimum sothat the bearing generates a minimum amount of heat. Another object isto provide a bearing from which heat is dissipated rapidly. A furtherobject is to provide a bearing having an optimum amount of internalstiffness. Still another object is to provide a bearing which is ideallysuited for use in precision machine tools and particularly for thespindles in such machine tools. These and other objects and advantageswill become apparent hereinafter.

The present invention is embodied in a tapered roller bearing having acup and cone provided with opposed raceways along which tapered rollersroll. At least one of the raceways is relieved to form a depression sothat full line contact between the roller side face and the raceway isavoided. The invention also consists in the parts and in thearrangements and combinations of parts hereinafter described andclaimed.

DESCRIPTION OF THE DRAWINGS In the accompanying drawings which form partof the specification and wherein like numerals refer to like partswherever they occur:

FIG. 1 is a sectional view of a bearing constructed in accordance withand embodying the present invention;

FIG. 2 is an enlarged fragmentary sectional view of the bearing; and

FIG. 3 is a fragmentary sectional view taken along line 3-3 of FIG. 2.

DETAILED DESCRIPTION Referring now to the drawings (FIG. 1), 2designates v a tapered roller bearing which supports a shaft 4 in ahousing 6. In actual practice, usually two bearings 2 are employed andthese bearings are mounted in opposition so that one can be adjustedagainst the other to eliminate axial and radial play in both bearings 2.The opposed mounting of tapered roller bearings is a conventionalpractice and, therefore, will not be illustrated or discussed further,other than to note that it enables the shaft 4 to carry axial loads inboth directions as well as radial loads.

In order to mount the tapered roller bearing 2 in opposition withanother tapered roller bearing 2, the shaft 4 is provided with ashoulder 8 against which'one end of the bearing 2 abuts, while thehousing 6 is provided with a cylindrical recess 10 terminating at ashoulder 12 against which the other end of the bearing 2 abuts. Thebearing 2 fits, or more-specifically, is seated, within the recess 10.

The housing 6 may be the headstock of a precision lathe, grinder,or'other machine tool, while the shaft 4 may be the spindle of such alathe or machine tool. As previously noted, in machine tools of thisnature, the temperature of the headstock and spindle is an importantconsideration, and that temperature must not fluctuate appreciably whilethe machine tool operates, for if it does .the machine tool willexperience dimensional changes will create errors in tooling set-ups.Moreover, the temperature of the headstock and spindle should remainclose to room temperature during operation of the machine tool so thattooling set-ups and workpiece changes may be made while the machine isat room temperature. In order to accomplish the foregoing the spindlebearings in the headstock should produce a minimal amount of heat andany heat which is produced should be dissipated rapidly.

The bearing 2 includes (FIG. 2) a cone 20, a cup 22 encircling the cone20, a set of tapered rollers 24 interposed between the cone 20 and cup22, and a cage 26 also disposed between the cone 20 and cup 22 andseparating as well as retaining the rollers 24. The cone 20, of course,fits around the shaft 4 and against the shoulder 8 thereon, while thecup 22 is press fitted into the cylindrical recess 10 with its one endor back face abutting against the shoulder 12. The cone 20 of courseconstitutes the inner race of the bearing 2, while the cup 22 forms theouter race. The cup 22 may also be loose fitted into the recess 10, inwhich case an end plate 27 should be used to clamp it in place (FIG. 2,phantom lines).

The cone 20 has (FIGS. 2 and 3) an outwardly presented tapered raceway28 which is engaged by the frustoconical side faces of the rollers 24.At the small diameter end of the raceway 28 the cone 20 is provided withan integrally formed retaining rib 30 for preventing the rollers 24 fromsliding axially off of the cone 20 when the cone 20 is removed from thecup 22. At the large diameter end of its tapered raceway 28 the cone Thetapered raceway 28 extends up to and ter-' minates at each rib 30 and32, but is not continuous between the ribs 30 and 32. On the contrary,the raceway 28 is relieved between its sides, or more specifically thecone 20 is provided with a shallow circumferential groove 36 whichdisposed between the sides of the raceway 28 so that the raceway 28 isdivided into two segments, one of which is positioned adjacent to theretaining rib 30 and the other of which is positioned adjacent to thethrust rib 32. The two segments of the raceway 28 lie in the samereference cone, and that cone has its apex along the common axialcenterline of the bearing 2 and the shaft 4.

As in conventional tapered roller bearings, the cage 26 hassubstantially rectilinear pockets which receive the rollers 24, but aresmaller in width than the'diameter of the received rollers 24 so thatthe rollers 24 will project beyond the cage 26 yet cannot be withdrawnoutwardly from cone 20. Consequently, the cage 26 in conjunction withthe ribs 30 and 32 retains the rollers 24 on the cone 20.

The cup 22 has (FIGS. 2 and 3) a tapered raceway 40 which is presentedinwardly toward the cone raceway 28 and is likewise engaged by thefrustoconical side faces of the rollers '24. Thus, the rollers 24 rollalong both the raceways 28 and 40 as they revolve within the cup 22 andabout the'cone 20. Likethe cone raceway 28, the cup raceway 40 isrelieved or interrupted, that is to say it is divided into two segmentsby a shallow circumferential groove 42 which is disposed between thesides of the raceway 40 and is located generally opposite to the groove36 in the cone raceway 28. Accordingly, the cup raceway 40 engages thefrustoconical side faces of the rollers 24 near the ends thereof, butdoes not engage the side faces of the rollers along the centralpositions thereof. The two segments of the raceway 40 lie in the samereference cone, andthat reference cone has its apex along the commoncenterline of the bearing 2 and shaft 4 at the point thereon where theapex of the reference cone defining the cone raceway 28 is located.

On its opposite side the cup 22 is provided with a plurality of axiallyspaced annular channels 44 which open radially outwardly. Since the cup22 is snugly fitted into the cylindrical recess of the housing 6, theopen sides of the channels 44 are covered by the cylindrical side wallof the recess 10, thus forming closed coolant channels around the cup22. When the cup 22 is press fitted into the recess 10 the snugness ofthe fit alone is enough to create an adequate seal for the channels 44.When a loose fit is employed the end plate 27 provides a suitable seal.The coolant channels 44 are supplied with a liquid coolant through aduct 46 (FIG. 1) in the housing 6 and a supply manifold 48 at the innerend of the duct 46. The supply manifold 48 is merely a relief whichextends across all of the annular channels 44 so that the coolant can bedistributed to those channels 44. The coolant which enters the supplymanifold 48 enters the annular channels 44 and flows around the cup 22,and in so doing absorbs heat therefrom. The coolant leaves the annularchannels 44 at a discharge manifold 50 located opposite to the supplymanifold 48 and a return duct 52 leading away from the manifold 50.

As the shaft 4 rotates with respect to the housing 6, the cone 20, ofcourse, rotates within 'the cup 22. The tapered rollers 24, in turn,being positioned between and engaged with the raceways 28 and 40 of thecone 20 and cup 22, respectively, roll'along those raceways. Moreover,the large diameter end faces of the rollers 24 bear or slide against theinside face 34 of the thrust rib 32, andaccordingly the thrust rib 32positions the rollers 24 axially with respect to the cone 20. Since, thecontact between the end faces of the rollers 24 and the inside face 34of the thrust rib 32 is sliding in nature a thin film of lubricant mustbe maintained between those opposed faces to prevent failure anddestruction of the bearing. Lubricant also is introduced to the raceways28 and 40, and is worked along those raceways by the rollers 24.

The presence of the shallow grooves 36 and 42 in the raceways 28 and 42,respectively prevents full line contact between the frustoconical sidesurfaces of the rollers 24 and the cone 20 and cup 22. This, in turn,reduces the elastohydrodynamic oil film resulting from the presence ofthe lubricant on the raceways 28 and 40 to an absolute minimum. In otherwords, the clastohydrodynamic oil film is confined entirely to therelatively short lines of contact between the raceways 28 and 40 and thefrustoconical side faces of the rollers 24. In this connection, itshould be noted that the depth of the grooves 36 and 42 exceeds thethickness of the elastohydrodynamic oil film. The lines of contact donot extend the full length of the rollers 24 as is true in conventionaltapered roller bearings, but on the contrary are only at the ends of therollers.

Since the elastohydrodynamic oil film between the rollers 24 and theraceways 28 and 40 is greatly reduced, the heat generated in creatingand maintaining it is also reduced in comparison to conventional taperedroller bearings. Consequently, the bearing 2 produces relatively littleheat in operation. Moreover, much of the heat which is generated iscarried away in the coolant which is circulated through the annularcoolant channels 44 extending around the cup 22. As a result, thebearing 2 tends to operate near room temperature, and there is not asignificant rise in temperature during initial or subsequent periods ofoperation. This makes the bearing 2 ideally suited for use in precisionmachinery and particularly suitable for the spindles of precisionmachine tools.

Stated differently, in the bearing 2 or for that matter any otherrolling element bearing a hydrodynamic oil film is created by thesurface motion of the rolling elements. When this hydrodynamic film iscompressed between the rolling elements and another surface, namely thebearing raceways, an elastohydrodynamic oil film developes. The creationof the clastohydrodynamic oil film requires work or energy, and theenergy so provided appears as heat within the oil film, causing thetemperature of the oil film and bearing to rise.

In the bearing 2 the depth of the grooves 36 and 42 is greater than thethickness of the elastohdrodynamic oil film, and consequently noelastohydrodynamic film develops along the grooves 36 and 42. Indeed,the elastohydrodynamic oil film is confined only to the relativelynarrow raceway segments or bands located to the sides of the grooves 36and 42. As a result the heat generated in producing theelastohydrodynamic oil film in the bearing 2 is significantly less thanthe heat generated in bearings of equivalent size having full linecontact between their rollers and raceways.

Since the rollers 24 are relatively long, or at least as long as rollersin comparable tapered roller bearings of conventional design, therollers 24 remain stabilized between the raceways 28 and 40 insofar asthe orientation or axial disposition is concerned. In other words, therollers 24 avoid skewing with respect to the raceways 28 and 40 byreason of their conventional length, and this reduces the introductionof inaccuracies in the bearing 2 and in the disposition of the shaft 4as the shaft 4 rotates. indeed, the rollers 24 possess considerably morestability then do short rollers of equivalent, yet full line, contactlength. Furthermore, the presence of the circumferential grooves 36 and42 in the raceways 28 and 40 and the resulting spreading of the contactareas along the raceways 28 and 40 provides increased rigidity for supporting the shaft 4 when compared to conventional bearings having shortrollers of equivalent, yet full line, contact length.

In machine tools the cutting characteristics of the tool are related tothe stiffness and the damping characteristics of the hearings in whichthe tools spindle turns. Moreover, with rolling element bearings inwhich machine tool spindles turn, heat generation is directly related tostiffness. Since stiffness and damping characteristics of such bearingsare related to the rollerraceway contact length, by varying the contactlength or more specifically the width of the raceway grooves 36 and 42an optimum condition of bearing stiffness, damping and heat generationmay be reached for the operating requirements of a particular machinetool.

While the foregoing discussion has been confined to single row taperedroller bearings to simplify the description, it may also be used withdouble row tapered roller bearings. Moreover, the cone may encircleannular channels similar to the annular channels 44, in which case itwill be cooled in a like manner.

This invention is intended to cover all changes and modifications of theexample of the invention herein chosen for purposes of the disclosurewhich do not constitute departures from the spirit and scope of theinvention.

What is claimed is:

l. A tapered roller bearing comprising a cone having an outwardlypresented raceway, a cup surrounding the cone and having an inwardlypresented raceway located opposite to the cone raceway, and rollersinterposed between the cup and the cone and having frustoconical sidefaces engaged with the raceways of the cup and cone, each of theraceways being relieved to form a depression therein so as to avoid fullline contact between the frustoconical side faces of the rollers and therelieved raceways. I

2. A tapered roller bearing according to claim 1 wherein the depressionin each raceway is located intermediate its sides and is narrower thanthe length of the rollers, whereby the rollers engage the raceways onboth sides of the depressions therein.

3. A tapered roller bearing according to claim 2 wherein the depressionsin the raceways are grooves extending around the raceways.

4. A tapered roller bearing according to claim 3 wherein the cup isprovided with at least one channel in which a fluent cooling mediumcirculates.

5. A tapered roller bearing according to claim 4' wherein the channel isannular and opens radially outwardly from the cup.

6. A tapered roller bearing according to claim 5 wherein the cup isprovided with a plurality of channels located in axially spaced relationto each other across the outwardly presented face of the cup.

7. A tapered roller bearing comprising: a cone having an outwardlypresented raceway along which an oil film exists; a cup surrounding thecone and having an inwardly presented raceway along which an oil filmalso exists, the cup raceway being located opposite to the cone raceway;and tapered rollers interposed between the cup and the cone and havingfrustoconical side faces engaged with the raceways of the cup and conewhereby an elastohydrodynamic oil film is created as the rollers rollalong' the raceways; both raceways defining cones having their apexesalong the axis for the bearing; at least one of the raceways beingrelieved to form a groove which extends circumferentially around thatraceway so that full line contact between the frustoconical side facesof the rollers and the grooved racewayis avoided, the depth of thegroove being greater than the thickness of the elastohydrodynamic oilfilm.

8. A tapered roller bearing comprising an inner race having an outwardlypresented tapered raceway defining a cone, the apex of which lies alongthe axis of the bearing; an outer race surrounding the inner race andhaving an inwardly presented raceway located opposite to the raceway ofthe inner race and also defining a cone, the apex of which lies alongthe axis of the bearing; at least one of the races having an annulargroove between the ends of its raceway for dividing that raceway intotwo annular segments; tapered rollers interposed between the two racesand having frustoconical side faces engaged with the raceways, therollers spanning the groove in said one race so as to engage the racewaysegments on both sides of the groove, whereby full line contact betweenthe frustoconical side faces of the rollers and said one race is avoidedand when a lubricant exists within the bearing the elastohydrodynamicoil film resulting therefrom is reduced; and a cage for spacing adjacentrollers.

9. A tapered roller bearing according to claim 8 wherein the depth ofthe groove exceeds the thickness of the elastohydrodynamic oil film.

10. A method for reducing heat generated in the operation of alubricated roller bearing having races with opposed raceways thereon androllers between the races and engaged with the raceways, said method andthe segmented raceway, whereby an elastohydrodynamic oil film does notdevelop along the groove as the one race rotates relative to the otherrace and the rollers roll along the raceways.

1. A tapered roller bearing comprising a cone having an outwardlypresented raceway, a cup surrounding the cone and having an inwardlypresented raceway located opposite to the cone raceway, and rollersinterposed between the cup and the cone and having frustoconical sidefaces engaged with the raceways of the cup and cone, each of theraceways being relieved to form a depression therein so as to avoid fullline contact between the frustoconical side faces of the rollers and therelieved raceways.
 2. A tapered roller bearing according to claim 1wherein the depression in each raceway is located intermediate its sidesand is narrower than the length of the rollers, whereby the rollersengage the raceways on both sides of the depressions therein.
 3. Atapered roller bearing according to claim 2 wherein the depressions inthe raceways are grooves extending around the raceways.
 4. A taperedroller bearing according to claim 3 wherein the cup is provided with atleast one channel in which a fluent cooling medium circulates.
 5. Atapered roller bearing according to claim 4 wherein the channel isannular and opens radially outwardly from the cup.
 6. A tapered rollerbearing according to claim 5 wherein the cup is provided with aplurality of channels located in axially spaced relation to each otheracross the outwardly presented face of the cup.
 7. A tapered rollerbearing comprising: a cone having an outwardly presented raceway alongwhich an oil film exists; a cup surrounding the cone and having aninwardly presented raceway along which an oil film also exists, the cupraceway being located opposite to the cone raceway; and tapered rollersinterposed between the cup and the cone and having frustoconical sidefaces engaged with the raceways of the cup and cone whereby anelastohydrodynamic oil film is created as the rollers roll along theraceways; both raceways defining cones having their apexes along theaxis for the bearing; at least one of the raceways being relieved toform a groove which extends circumferentially around that raceway sothat full line contact between the frustoconical side faces of therollers and the grooved raceway is avoided, the depth of the groovebeing greater than the thickness of the elastohydrodynamic oil film. 8.A tapered roller bearing comprising an inner race having an outwardlypresented tapered raceway defining a cone, the apex of which lies alongthe axis of the bearing; an outer race surrounding the inner race andhaving an inwardly presented raceway located opposite to the raceway ofthe inner race and also defining a cone, the apex of which lies alongthe axis of the bearing; at least one of the races having an annulargroove between the ends of its raceway for dividing that raceway intotwo annular segments; tapered rollers interposed between the two racesand having frustoconical side faces engaged with the raceways, therollers spanning the groove in said one race so as to engage the racewaysegments on both sides of the groove, whereby full line conTact betweenthe frustoconical side faces of the rollers and said one race is avoidedand when a lubricant exists within the bearing the elastohydrodynamicoil film resulting therefrom is reduced; and a cage for spacing adjacentrollers.
 9. A tapered roller bearing according to claim 8 wherein thedepth of the groove exceeds the thickness of the elastohydrodynamic oilfilm.
 10. A method for reducing heat generated in the operation of alubricated roller bearing having races with opposed raceways thereon androllers between the races and engaged with the raceways, said methodcomprising: reducing the elastohydrodynamic oil film between the rollersand at least one of the races by providing said one race with an annulargroove between the ends of its raceway so that the raceway is dividedinto spaced apart annular segments and full line contact does not existbetween the sides of the rollers and the segmented raceway, whereby anelastohydrodynamic oil film does not develop along the groove as the onerace rotates relative to the other race and the rollers roll along theraceways.